The enclosed proposal is requesting funds to expand the mass spectrometry and proteomics resources at the University of Washington through the purchase of a ThermoFinnigan LTQ-FT mass spectrometer. This instrument will be invaluable in the successful completion of our existing NIH funded projects involving the qualitative and quantitative analysis of proteins and protein modifications of complex mixtures. Furthermore, a number of our projects are extending quantitative proteomics technology to the measurement of changes in the rate of protein expression and degradation (protein dynamics). Integral to the timely completion of these NIH research projects is the availability of a mass spectrometer capable of i) sub 2 ppm mass accuracy to distinguish between similar mass peptides, ii) a dynamic range of >1000 in a single spectrum, iii) data-dependent acquisition of tandem mass spectra with the sensitivity and speed of a quadrupole ion trap, and iv) the ability to resolve and detect unusual isotope distributions of multiply charged peptides within a complex mixture. No such shared instrument is available to investigators at the University of Washington and several of our Users travel to outside laboratories to complete their NIH funded projects. Although we have managed to work around the lack of availability of a mass spectrometer capable of these measurements we cannot continue in this way if we hope to remain productive and competitive. We propose to address these limitations through the acquisition of a shared hybrid mass spectrometer which combines the robustness and speed of a linear quadrupole ion-trap with the resolution, mass accuracy, and dynamic range of a Fourier transform ion cyclotron mass spectrometer. The performance of the requested instrumentation will allow the faculty to address current technological limitations on a global level and will provide a resource that is not available within the university.